The present invention relates to a class of new and novel furnace carbon blacks which are suitable for various applications and particularly well suited for use in rubber compositions. The carbon blacks of the present invention impart improved hysteresis loss and abrasion resistance to rubber compositions, particularly passenger car tires, in which they are incorporated.
Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black.
Carbon blacks may be utilized as pigments, fillers, reinforcing agents and for a variety of other applications. For example, carbon blacks are widely utilized as fillers and reinforcing pigments in the compounding and preparation of rubber compositions.
Carbon blacks for rubber use have a variety of grades depending upon their properties and are generally classified on the basis of analytical properties including: surface area, structure (DBP absorption) and the like. Methods of measuring the surface area of carbon black include an electron microscope, nitrogen surface area (N2SA) according to the BET method, CTAB surface area according to the adsorption of cetyltrimethylammonium bromide as a surfactant, and iodine adsorption number (I2 No.). The structure of a carbon black refers to the linkage of carbon black particles due to agglomeration. As the degree of agglomeration becomes greater, the value of this structure becomes higher.
The properties of the grade of carbon black become an important factor in determining various performances of the rubber composition wherein the carbon blacks are incorporated. Carbon blacks are effective in the preparation of rubber vulcanizates intended for usage in preparing tires. It is generally desirable in the production of tires to utilize carbon blacks which impart high levels of abrasion resistance and low levels of rolling resistance to the tires.
The grade of the carbon black used mainly for tire treads is classified into HAF (high abrasion furnace), ISAF (intermediate super abrasion furnace) and SAF (super abrasion furnace) with SAF carbon black having a higher surface area than ISAF carbon black which has a higher surface area than HAF carbon black. Abrasion resistance generally improves as surface area increases.
The properties of the grade of carbon black become an important factor in determining various performances of the rubber composition wherein the carbon blacks are incorporated. Generally, carbon blacks having a specific surface area higher than ISAF are used for tire treads of trucks and buses wherein natural rubber is used as a main component. HAF type carbon blacks are used for passenger car tire treads wherein synthetic rubbers such as styrene butadiene rubber (SBR) are used as a main component.
Higher surface area carbon blacks impart improved abrasion resistance to tires. However, as specific surface area becomes larger, heat build-up of the rubber compound becomes higher and hysteresis becomes greater. The hysteresis of the compounds means the difference between the energy applied to deform a rubber compound, and the energy released as the rubber compound recovers to its initial undeformed state. Tires with lower hysteresis values have reduced rolling resistance and therefore reduce the fuel consumption of the vehicle utilizing the tire.
Thus it would be desirable to develop a carbon black which would impart both improved abrasion resistance and reduced hysteresis to rubber compounds. Tires prepared with such a carbon black would have lower rolling resistance, to improve the fuel economy of the vehicle utilizing the tire, and improved abrasion resistance, to reduce the tread wear of the tire.
One advantage of the present invention is the production of new carbon blacks which impart increased abrasion resistance and reduced hysteresis properties to natural rubbers, synthetic rubbers and blends of natural and synthetic rubbers incorporating the carbon blacks.
Another object of the present invention is new rubber compositions, advantageous for use as passenger car tires, incorporating the new carbon blacks.
Other objects of the present invention will become apparent from the following description and the claims.
We have discovered a new class of carbon blacks having a CTAB (cetyltrimethylammonium bromide adsorption value) of from about 65 m2/g (square meters per gram) to about 85 m2/g; a DBP (dibutyl phthlate absorption number) of from about 130 cc/100 g (cubic centimeters per 100 grams) to about 160 cc/100 g, a ratio of CTAB to I2 No. (iodine adsorption number) of from about 1.15 to about 1.35, a xcex94DBP (difference between DBP and Crushed DBP) of from about 20 cc/100 g to about 40 cc/100 g, a Tint value of from about 85 to about 100, a Dmode of from about 115 nm (nanometers=metersxc3x9710xe2x88x929) to about 135 nm and / D50/Dmode ratio of from about 0.65 to about 0.90. We have also discovered a new class of rubber compositions containing these carbon blacks.
Referring to the blacks of the present invention, when the CTAB exceeds about 85 m2/g, the improvement in hysteresis loss is reduced. When the CTAB is below about 65 m2/g the reinforcing properties of the carbon black are reduced and a good rubber composition cannot be obtained. Similarly, when the DBP of the carbon blacks of the present invention is below about 130 cc/100 g the reinforcing properties of the carbon blacks are unsatisfactory. When DBP exceeds about 160 cc/100 g the modulus of a rubber composition incorporating the carbon black is raised and the stiffness of the rubber composition is increased to disadvantageous levels.
When the difference (xcex94DBP=DBPxe2x88x92CDBP) between the DBP and the CDBP (dibutyl phthlate absorption number of the crushed carbon black) exceeds about 40 cc/100 g, the breakage of structure is raised to a point wherein the reinforcing property of the carbon black is disadvantageously reduced. When xcex94DBP is below about 20 cc/100 g the dispersibility of the carbon blacks is reduced and the ability of the carbon blacks to be mixed or incorporated into the rubber composition is disadvantageously reduced.
The ratio of CTAB to I2 No. (CTAB/I2No.) is a measure of surface chemical activity. The larger the CTAB/I2NO. ratio, the higher the chemical surface activity. With respect to the carbon blacks of the present invention when the CTAB/I2No. ratio is about 1.15 to about 1.35, it is found that the reinforcing property and hysteresis loss of rubber compounds is improved.
These effects are presumably caused by an interaction between the rubber and carbon black based on the surface chemical activity.
When the Tint value of the carbon blacks of the present invention exceeds about 100 hysteresis loss is disadvantageously increased-to an unacceptable level. When the Tint value is below about 85 the reinforcing properties of the carbon blacks are disadvantageously reduced to an unacceptable level.
When the Dmode of the carbon blacks of the present invention, according to the centrifugal sedimentation method described below, is less than about 115 nm, hysteresis loss is disadvantageously increased to an unacceptable level. When the Dmode is above about 135 nm the reinforcing properties of the carbon blacks are disadvantageously reduced to an unacceptable level.
When the xcex94D50/Dmode ratio is less than about 0.65, hysteresis loss is disadvantageously increased to an unacceptable level. When xcex94D50/Dmode ratio exceeds 0.90 the reinforcing properties of the carbon blacks are disadvantageously reduced to an unacceptable level.
However, we have discovered that the carbon blacks of the present invention, having analytical properties within the ranges specified, impart improved reinforcing properties and low hysteresis loss to rubber compositions. As explained above, the improved reinforcing properties of the carbon blacks impart improved abrasion resistance to rubber compositions.
The carbon blacks of the present invention may be produced in a furnace carbon black reactor having a first (combustion) zone, and a reaction zone separated by a transition zone, into which all or part of a carbon black yielding feedstock may be injected into a hot combustion gas stream. The carbon black yielding-feedstock is injected radially inwardly into the hot combustion gas stream from the outer periphery of the reactor and also radially outwardly injected from the center portion. The resultant mixture of hot combustion gases and feedstock passes into the reaction zone. A first quench may be used to cool the hot combustion gas stream, without stopping pyrolysis of the feedstock. Pyrolysis, of the carbon black yielding feedstock, is stopped by quenching the mixture when the carbon blacks of the present invention have been formed. Preferably pyrolysis is stopped by a quench injecting a quenching fluid, which in the Examples is water. A reactor suitable for use in producing the carbon blacks of the present invention is described generally in U.S. Pat. No. 3,922,335, the disclosure of which is hereby incorporated by reference. The process for preparing the novel carbon blacks of the present invention will be described in greater detail hereinafter.
The rubbers for which the novel carbon blacks of this invention are effective as reinforcing agents include natural and synthetic rubbers. Generally, amounts of the carbon black product ranging from about 10 to about 250 parts by weight can be used for each 100 parts by weight of rubber in order to impart a significant degree of reinforcement. It is, however, preferred to use amounts varying from about 20 to about 200 parts by weight of carbon black per 100 parts by weight of rubber and especially preferred is the utilization of from about 30 to about 100 parts of carbon black per 100 parts of rubber.
Among the rubbers suitable for use with the present invention are natural rubber and its derivatives such as chlorinated rubber; copolymers of from about 10 to about 70 percent by weight of styrene and from about 90 to about 30 percent by weight of butadiene such as copolymer of 19 parts styrene and 81 parts butadiene, a copolymer of 30 parts styrene and 70 parts butadiene, a copolymer of 43 parts styrene and 57 parts butadiene and a copolymer of 50 parts styrene and 50 parts butadiene; polymers and copolymers of conjugated dienes such as polybutadiene, polyisoprene, polychloroprene, and the like, and copolymers of such conjugated dienes with an ethylenic group-containing monomer copolymerizable therewith such as styrene, methyl styrene, chlorostyrene, acrylonitrile, 2-vinyl-pyridine, 5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine, 2-methyl-5-vinylpyridine, alkyl-substituted acrylates, vinyl ketone, methyl isopropenyl ketone, methyl vinyl ether, alphamethylene carboxylic acids and the esters and amides thereof such as acrylic acid and dialkylacrylic acid amide; also suitable for use herein are copolymers of ethylene and other high alpha olefins such as propylene, butene-l and penetene-1; particularly preferred are the ethylene-propylene copolymers wherein the ethylene content ranges from 20 to 90 percent by weight and also the ethylene-propylene polymers which additionally contain a third monomer such as dicyclopentadiene, 1,4-hexadiene and methylene norbornene.
An advantage of the carbon blacks of the present invention is that the carbon blacks impart increased abrasion resistance and lower hysteresis to compositions containing natural rubbers, synthetic rubbers or blends thereof in which the carbon blacks of the present invention are incorporated.
An advantage of the rubber compositions of the present invention is the that the rubber compositions are particularly well suited for use as passenger car tires.
Other advantages of the present invention will become apparent from the following more detailed description of the invention.